Screens or grilles are sometimes used to improve the security of a building. For example, steel bar grilles have been used to deter intruders from entering a premises through a window or door. When used for a window the steel bar grilles are bolted to a wall surface adjacent the window. When used for a doorway the steel bar grilles are pivotally mounted to the doorway and operate as an extra door.
Steel bar grilles are generally considered unsightly and are therefore usually only used for industrial buildings, shops and some places of business. Furthermore, the spacing between the steel bars of the grilles is usually wide enough to allow bolt cutters or hacksaws to cut the bars and therefore such grilles do not always provide adequate security.
An alternative to steel bar grilles are security screens which are often used to deter intruders from entering a premises through a window or door. Security screens comprise an extruded frame with a wide grate mesh covering the area enclosed by the extruded frame. The wide grate mesh typically has elongate members of 7 mm diameter with mesh gaps of approximately 60 mm. The mesh is normally fitted into a slot in the frame and is not usually clamped to the frame. One reason for this is because the wide grate mesh is usually made from expanded aluminium which is not suited to bolting due to the spaced small surface areas of the mesh which contact the frame. In addition, the contours of the mesh would require accurate and specific alignment of bolt holes for each screen which is labour intensive. Accordingly, it is possible for a potential intruder to remove the unbolted mesh partly or completely from the frame.
Such security screens also suffer from the same disadvantages as steel bar grilles in that the mesh can be cut by bolt cutters or hacksaws.
The above described screens or grilles can provide limited security even when their associated window or door is opened for ventilating a premises. However, these screens or grilles are not effective for insect screening and therefore fine mesh screens are sometimes used in conjunction with security screens or grilles for the purpose of insect screening. The fine mesh is usually either mounted to a wooden frame or mounted to a spline of the extruded frame of the screen in which a rubber strip is used to maintain edges of the mesh in the spline.
The above fine mesh screens are not intruder resistant as the wooden frame can be easily broken or the mesh can be easily removed from the spline. Furthermore, the fine mesh which is used is often made of thin nylon or thin metal strands which can be easily broken. Accordingly, to provide limited security and insect screening both fine mesh screens and security screens or grilles are often used which has the disadvantage of increased manufacturing or installation costs.
Examples of either security screens or insect screens can be found in the prior art. The prior art does not provide screens which are both insect screening and of sufficient strength to prevent entry by undesirable persons.
One prior art example is U.S. Pat. No. 1,588,161, in the name of Bost. Bost teaches a small metal frame that frictionally holds screen wire. The screen wire is held in a recess (or spline as described above) by a hard cord which is pressed into the recess. The screen wire must be malleable so that it can be easily deformed to line the recess and permit further deformation upon insertion of the cord. Bost also discloses a plate that covers the cord and recess to give the frame a suitable appearance.
Bost does not disclose a screen of sufficient strength to prevent entry by intruders nor a method of securing a suitable screen to the frame. A screen having sufficient strength to provide intruder resistance will not be malleable in the manner required to implement the cord and recess clamping arrangement of Bost.
A similar arrangement is disclosed in U.S. Pat. No. 3,220,469, in the name of Oehmig. Oehmig describes an improved screen in which the mesh is retained in a mounting pocket and a molding strip snaps over the mounting pocket to improve the appearance. Like Bost the screen is malleable to facilitate retention of the screen in the mounting pocket by a push-in bead. Oehmig also describes the option of incorporating the bead into the molding strip.
As with Bost, the clamping arrangement of Oehmig can not provide sufficient strength to hold a screen that will provide intruder resistance. Furthermore, a mesh sufficiently malleable to deform into the mounting pocket can not have sufficient strength to provide a barrier to entrance by burglars.
U.S. Pat. No. 5,141,046, in the name of Duncan, relates to the use of screens for security and/or to resist vandalism. Duncan acknowledges that a mesh having intruder resistant properties can not be deformed in the manner required for the conventional fastening methods described above. Duncan describes the use of a flat retainer bar that clamps the mesh to the frame and is fastened by two lines of screws. Although an improvement over the prior art, Duncan still fails to provide sufficient holding strength to retain the mesh in the frame when attacked by a determined intruder.